The present invention relates to a method of selectively and variably positioning tubing within and along substantially the entire length of the generally horizontal section of a horizontally drilled well, and more particularly, to a method for stimulating and/or treating the horizontal section of a horizontally drilled well.
In recent years, horizontally drilled wells have been increasingly utilized to recover significant amounts of liquid hydrocarbons from fractured subterranean hydrocarbon-bearing formations. In drilling a horizontal well bore, a generally vertical well bore is first drilled from the surface to a depth approximating the subterranean hydrocarbon-bearing formation of interest. The well bore is then deviated through a curve section and terminated in a generally horizontal direction. In horizontal wells having medium to large radius of curvatures, i.e., greater than 16 meters, the well can be completed by positioning casing through the vertical and curve sections and into the horizontal section of the well bore. The casing is then cemented and the well is placed in fluid communication with the formation by any suitable means, such as, by perforating. In horizontal wells having a relatively small radius of curvature, e.g., less than 16 meters, casing cannot be cemented effectively through the curved section of the well bore, and accordingly, the generally horizontal section of the well bore is usually completed open hole, i.e. without cement casing.
Alternatively, a horizontal drainhole can be drilled from an existing vertical well which is usually cased. The casing of the vertical well is packed off and is provided with a whipstock. A portion of the casing above the whipstock is milled away to provide a window for drilling access. The whipstock assists the drill string which is equipped with flexible drill collars or the like in drilling the curve section. Directional survey tools can be used to locate the path of the subsequently drilled drainhole. As with newly drilled wells, drainholes having a relatively short radius of curvature cannot be completed with effectively cemented casing.
The use of a smaller diameter tubing string has been proposed to complete horizontally drilled wells having a relatively small radius of curvature. In accordance with this proposed technique, the tubing string is equipped with a bull plug or cap at the lower end thereof. This bull plug provides a rounded peripheral configuration which prevents the tubing from becoming stuck in the well bore walls of the curve section of the horizontal well and thus permits the tubing string to be positioned within the horizontal section of the horizontal well. However, the end of the tubing usually cannot be positioned at or near the end of the horizontal section of the horizontal well. Often the horizontal section of the well is incongruous and thus does not permit the tubing string to pass through the entire length. thereof. And since a tubing string is usually bent while passing through the short radius of curvature of a radius section of a horizontal well, the bent tubing string usually encounters the top of the well bore wall in the horizontal section of the well and becomes stuck. Also, a portion of the horizontal section of a horizontal well may be drilled upwardly into the gas cap of a subterranean hydrocarbon-bearing formation. In such instances, the tubing would be inserted only into that portion of the horizontal section of the well which exists within the oil-bearing zone of the formation. Thus, as the bull plug or cap prevents movement through the tubing, treatment of the horizontal section of a horizontal well bore existing beyond the end of tubing has been problematic. Therefore, a need exists for a method for selectively and variably treating that portion of the horizontal section of a horizontal well bore which extends beyond the end of tubing positioned within the horizontal section.
Accordingly, it is an object of the present invention to provide a method for selectively and variably placing tubing within the generally horizontal section of a horizontally drilled well.
It is a further object of the present invention to provide a method for stimulating and/or treating the generally horizontal section of a horizontally drilled well.